1. The problem statement, all variables and given/known data Have a design project in thermodynamics. The problem reads, Someone has suggested that the device shown in the figure below be used to improve the maximum force F against the spring, which has a spring constant of k. This is accomplished by changing the temperature of the liquid-vapor mixture in the container. You are to design such a device to close sun-blocking window-shutters that require a maximum force of 0.5 lbf. The piston must move 6 inches to close those shutters completely. You elect to use R-134a as the working fluid and arrange the liquid-vapor mixture container such that he temperature changes from 70 degrees F when shaded from the sun to 100 degrees F when exposed to the full sun. Select the sizes of the various components in this system to do this task. Also select the necessary spring constant and the amount of R-134a to be used. 2. Relevant equations Force=pressure*Area Force=k*x 3. The attempt at a solution All of my work and all the info I have been using is in the attachments. I have been working it on a whiteboard at school. I can only load 3 pics. I continued on and found that the natural length of the spring is 9.707 inches with a k value of 0.031833 Lbf/in. I am assuming that at 100 degrees F that the system is in equilibrium and the force to keep the windows closed is 0.5 lbf. The picture also shows the piston is closed off, so I am assuming that I don't need to worry about atmospheric pressure. I can't see where I am going wrong, but the piston diameter seems to small. Is this right or am I reading the original problem wrong.